Finally built this thing for the mane instead of just buying one.  There was a dream of making an artistic voronoi pattern, but after burning $3 of filament on testing the sizing, the prototype was close enough to not have any incentive to print another one.  Shampoo bottles vary in size.

A quick goog showed there is no shower caddy designed to stand shampoo bottles upside down & what China does produce is expensive.  Maybe there's a need to do it right.

The trick with voronoi patterns is to 1st create surfaces with the required dimensions in Freecad.  The loft tool allows you to create hollow tubes.  Extruding an open line creates a surface.  The only way to get a plane from a closed line is to extrude & delete unwanted faces in blender.  There's no sketch to plane command.

The voronoi pattern is created by tesselating it.  The way to tesselate it is

Mesh Design workbench -> tesselate -> netgen -> fineness: very coarse

View it in wireframe mode to see the pattern.

Then the mesh is exported to an STL file & loaded in blender.  

There's a manual step in edit mode which creates holes in the triangles.

The trick is to select all the vertices which are to be converted to holes.  Select the edge loop & invert.  There's no need for a vertex group.

Then enter face select mode.

Vertex -> bevel vertices in face select mode causes it to select the newly created faces.  Width type has to be percent.  Percentage has to be 45.

Then we do a delete -> faces only to create the holes.

Back in object mode, there's a subdivide modifier to smooth the holes  & solidify.  Subdivide uses catmull-clark, advanced->Boundary smooth->keep corners.  Solidify thickness was 2m.

It needs a lot of manual cleanup, but it gives the biological shape lion manes want.

Important when tesselating to avoid really small holes because they'll just crumble in the printout.  Sharp corners & mirrors create small holes.  You have to mirror the source sketch & merge sketches to get a symmetric surface the tesselator can tesselate.

 Cura has trouble leveling it so the bottom needs to be 2mm thick.  The model needs to be sunk by 1mm.

It took 3 tries to get the holes & surfaces right.

The result was a shampoo holder like no other.  This was printed in .32mm layers with the .8mm nozzle & finished in 7 hours.  .2mm layers with the .4mm nozzle would have taken over 1 day but obviously looked like glass.

There were problems with the overhangs & no practical way to use supports.  The solution might be a script to search for all overhangs over 45 deg & straighten them to 45 deg.  It would begin after  the bevel vertices operation, assigning the new faces to a vertex group, & running the script.

Printing .2mm layers with the .4mm nozzle would also improve the overhangs.

When the shampoo bottles change size, the trick is to just print the top edges to check the sizes, then print the whole thing.

Voronoi shampoo holder is the lion kingdom's 1st major foray into curved shapes.  The last attempt was the 2018 BFR.  It did not end well.  The ultimate test of curved shapes is the pterodactyl glider idea.